Synthesis of diverse cyclic-brush polymers with cyclic polystyrene as a universal template via a grafting-from approach

Abstract

Combining the ring-closure method with the “grafting from” method, a novel synthetic strategy for preparing cyclic-brush polymers with controlled grafting density was successfully demonstrated. The cyclic polystyrene (c-PS) precursor was synthesized using the general methods of activators generated by electron transfer for atom transfer radical polymerization (AGET-ATRP) and Cu-catalyzed azide–alkyne cycloaddition (CuAAC), and was well characterized using NMR, GPC, MALDI-TOF mass spectroscopy and FT-IR. The benzylic hydrogen atoms of c-PS were substituted with bromine based on Wohl–Ziegler bromination to generate a tertiary bromide ATRP macroinitiator (c-PSBr), and the bromine content can be adjusted to 18.4%, 25.3%, 31.9% and 50.3% by using different reaction conditions. This ATRP macroinitiator can also be converted into a macro-RAFT agent with azole (c-PSN) or ethyoxyl (c-PSO) as the Z groups based on the styrenic polymers as the R group. Using the as-prepared ATRP macroinitiator or macro-RAFT agents, a series of cyclic-brush polymers including c-PS-g-PS, c-PS-g-PNIPAM, c-PS-g-PMMA, c-PS-g-PMA and c-PS-g-PVAc were successfully prepared. The grafting density can be facilely tuned by using variable Br content of c-PSBr or Z group content of the macro-RAFT agents. The work illustrated a first example of versatile synthesis of cyclic-brush polymers with predictable molecular weight, grafting density and different grafting polymer chains.